Improve OpenSSL detection on CentOS with mixed setup of 1.0 and 1.1 versions

EPEL for CentOS install OpenSSL 1.1 in very peculiar way, which does not allow using OPENSSL_ROOT_DIR macro, because headers installed at /usr/include/openssl11 while libraries live at /usr/lib64/openssl11. CMake itself cannot detect this kind of setup, and if you point to right openssl11 headers, still tries to use OpenSSL 1.0 libraries during link phase.

As a solution, we must detect this unusable mix, and fallback to pkg-config path to detect OpenSSL. We don't want to use pkg-config by default, as cmake's FindPackage(OpenSSL) is preferred and more flexible way.